Known artificial discs are disclosed in U.S. Pat. Nos. 6,607,558; 7,128,761; and 7,169,181. These patents disclose artificial discs having retainers which are engagable with vertebrae. The retainers are connected with an intermediate section which is disposed between the retainers. Relative rotation between the vertebrae is resisted by the intermediate section of the artificial disc. The entire intermediate section of the artificial disc is effective to resist relative rotation between the vertebrae throughout the range of relative rotation between the vertebrae.